Over the past few years, a rapid increase in recording density has been pursued at an annual rate of approximately 40% for magnetic recording devices, such as hard disk drives (HDDs). Areal recording density is expected to reach 2 terabits (Tb)/in2. In order to improve the areal recording density, it is important to miniaturize the magnetic write head and the read head, and to reduce the particle size of the magnetic recording medium.
However, challenges with regard to inadequate recording performance are predicted because the magnetic write field strength is reduced by the miniaturization of the magnetic write head. In addition, the coercive force and the anisotropic energy of a magnetic recording medium must be increased simultaneously to reducing the particle size because the problem of thermal fluctuations arises when the particle size of the magnetic recording medium is reduced. As a result, recording becomes difficult. Consequently, it is necessary to improve recording performance in order to improve the areal recording density. One proposal is assisted recording that temporarily lowers the coercive force (reversal magnetic field) of the magnetic recording medium only during recording by applying heat or a high-frequency magnetic field.
Methods for applying a high-frequency magnetic field, sometimes referred to as microwave-assisted magnetic recording (MAMR), have gained attention over the past few years. In MAMR, information is recorded by applying a high strength, high frequency magnetic field in the microwave band to a region on the order of nanometers to locally excite the recording medium and lower the magnetization reversal magnetic field.